Satellite dish antennas are becoming increasingly popular for receiving signals from orbiting satellites. They are commonly used by consumers who receive television signals, and extensively used by the military and commercial firms for advanced telecommunication applications. They can be found in rural areas that are not served by cable television systems, military bases, and large corporate headquarters. They are also used for various recreational vehicles, such as motor homes, campers, trailers, and mobile homes.
Antenna dish systems vary in their size and can range from having a large antenna dish that is many meters wide to small, portable antenna dishes that are about one meter wide. Some of the antenna dish systems are also portable and can be collapsible to aid in mobility. These more mobile antenna dish systems can be especially adapted for use by the military, commercial news broadcasters and other commercial firms.
Typically, the antenna dish has a parabolic shape and uses heavy and sturdy mounting systems to prevent damage to the antenna dish and associated controls during wind storms. The parabolic geometry allows reflection and collection of signals at a particular point in space at a distance from the inner surface of the antenna.
Some of the antenna dish systems used for satellite communication systems have linear actuators that drive the antenna dish to track a satellite. Typically, a linear actuator has a line of action from its output shaft that is located a distance from the antenna axis rotation to provide a moment arm. Sometimes the linear actuator provides one suspension point for the antenna dish, while other suspension points might include ball joints or similar suspension joints. An example of various types of antenna dish mounting systems and drive mechanisms are disclosed in U.S. Pat. Nos. 4,251,819 to Bickland; 4,783,662 to Wirth, Jr., et al.; 4,814,781 to DeHaven; 5,355,145 to Lucas; 5,418,542 to Sherwood, et al.; and 5,512,913 to Staney.
The '819 patent to Bickland overcomes some of the prior problems in bulky pointing and tracking mechanisms by having three suspension points on the antenna, each suspension joint having two degrees of freedom of movement. This system does not use linear actuators, whose line of action is located a distance from the antenna axis of rotation. A top suspension point includes a ball joint that provides for rotational movement, but constrains movement in all other directions. Other linear supports, which can be vertically moveable, also provide for two degrees of movement, similar to the rotative movement of a ball joint. All suspension points are located toward the medial portion of the antenna dish. Because all suspension points provide for rotational movement, the system includes a stabilizing bar connected between the two vertical legs.
Some applications of antennas require only a low cost, small (one meter), narrow beam (about 1.0 degree) antenna satellite dish that acts as a ground receive terminal (GRS). Such an antenna dish system should be lightweight, have limited antenna dish motion, and be portable. These types of antenna dish systems typically have legs that can be pressed into the ground and then used for portable communications. Additionally, these antenna dish systems are center mounted, full motion pedestals having pointing errors resulting from backlash and compliance. Additionally, the structures are heavy and have a difficult time meeting the necessary pointing accuracy without being heavy and expensive to drive. Other antenna dish approaches used a single axis approach that suffered extreme inconvenience on the operator's part. Some of these expensive and very heavy systems allow a wide range of satellite dish movement.
However, in many portable antenna dish applications, using high frequency, narrow beam antenna dishes, only a limited motion is required for tracking geostationary satellites. Additionally, only very slow antenna dish movement rates are necessary. With these factors in mind, it is not necessary to use these prior art antenna dishes that are complicated, costly, have expensive and sturdy pedestals, and complicated positioning and tracking mechanisms that allow a wide range of antenna dish movement. Those advantages are not necessary for many portable ground receive terminals. Additionally, even some large fixed ground stations do not require large antenna dish movements, but only a limited motion of the antenna dish.
If limited motion and slow rates of antenna dish movement are the only factors necessary, it would be possible to reduce the cost by manufacturing a more simple antenna dish system that is lightweight, inexpensive, and minimizes backlash and compliance in a high wind buffeting while also using lightweight and lower cost small, slow speed linear actuators. However, it will often be necessary to constrain rotational movement in a more simplified system in order not to defeat the control that is being imparted, such as by the use of linear actuators.